The present invention generally relates to a knock control system for a supercharged internal combustion engine and, more particularly, to the control of both the ignition timing and the supercharged pressure in the event of occurrence of the engine knocking to minimize the reduction in performance of the engine.
U.S. Pat. No. 4,387,571, patented June 14, 1983, discloses the control of the supercharged pressure, being introduced into the engine cylinders, according to the intensity of the knocking occurring in the supercharged engine. The system disclosed therein generally comprises a supercharge control device designed either to allow a portion of exhaust gases to bypass the exhaust-driven turbine of the supercharger or to relieve a portion of supercharged air, being introduced past the supercharger compressor into the engine cylinder, to the atmosphere or back into the intake passage upstream of the compressor, means for detecting the frequency of occurrence of the knocking, and a control circuitry for controlling the supercharge control device in dependence on the frequency of occurrence of the knocking detected. According to this system, it is claimed that the minimization of occurrence of the heavy knocking thereby to avoid the failure of the engine to operate can be achieved by lowering the supercharged pressure in the event of occurrence of the knocking.
The engine knocking can be substantially eliminated, or minimized, not only by the control of the supercharged pressure such as hereinabove discussed, but also by the control of the ignition timing as is well known to those skilled in the art. In the case of the control of the ignition timing, the ignition timing is retarded in response to the occurrence of the engine knocking to achieve the intended purpose.
When it however comes to the simultaneous control of both the supercharged pressure and the ignition timing for the achievement of the intended purpose, Japanese Laid-open Patent Publication No. 58-72644, published Apr. 30, 1983, discloses a knock control system which comprises a knock sensor capable of generating a knock signal indicative of the occurrence of the knocking in the supercharged engine; an engine sensor capable of generating an engine signal indicative of an operating condition of the engine; a supercharge sensor capable of generating a supercharge signal indicative of the pressure of supercharged air flowing in the engine intake piping; a supercharge control means for controlling the supercharged air; an ignition timing control means for controlling the ignition timing; and a controller for generating a control output to both of the supercharge control means and the ignition timing control means in dependence on all of the knock signal, the engine signal and the supercharge signal. The controller used in this knock control system comprises a pressure comparison means for comparing the supercharged pressure detected by the supercharge sensor with a reference supercharge pressure calculated (or determined) in dependence on the intelligence derived from the engine signal; a timing comparison means for comparing the ignition timing detected by the ignition timing detector with a reference ignition timing calculated (or determined) in dependence on the engine operating condition and the supercharged pressure for giving the substantially highest possible engine torque; and a control unit.
The control unit referred to above is described as electrically connected with both of the supercharge control means and the ignition timing control means so that, when intelligence derived from a combination of the output signals from the respective pressure and timing comparison means has indicated that the supercharged pressure detected is equal to the reference supercharged pressure, the ignition timing can be controlled while the supercharged pressure is fixed at a value equal to the reference supercharged pressure, it being, however, that when as a result of the control of the ignition timing so effected the controlled ignition timing deviates from a predetermined range adjacent and retarded a predetermined angle from the reference ignition timing, the supercharged pressure can be controlled in dependence on the knock signal and regardless of the supercharge signal while the ignition timing is fixed at a timing falling within the predetermined range and retarded a predetermined angle relative to the reference ignition timing, but that, when the same intelligence has indicated that the supercharged pressure detected is lower than the reference supercharged pressure, the ignition timing can be controlled.
U.S. Pat. No. 4,463,565, patented Aug. 7, 1984, also discloses a similar knock control system, but it has been found having a problem in that, since as a matter of design the adjustment of the supercharged pressure does not quickly take place, while that of the ignition timing can take place relatively quickly, in response to the occurrence of the knocking, the ignition timing must be greatly retarded in order for the knocking to be quickly suppressed, with the consequence that the system as a whole is susceptible to the admission of heavy knocking particularly when the reduction in engine power output as a result of the adjusted ignition timing and that as a result of the adjusted supercharged pressure take place generally simultaneously. As is well known to those skilled in the art, the control of the supercharged air while the retardation of the ignition timing is minimized is preferred for the prevention of both the reduction in engine power output and the excessive increase of the exhaust temperature.